NEW ORLEANS (AP) — A patch of ground in southern Louisiana is being surveyed to see if it may hold a mass grave from a Reconstruction-era racial massacre.

A graduate student and a professor using ground-penetrating radar and limited coring will begin an initial survey Thursday in Thibodaux, where locals believe white mobs dumped the bodies of African-Americans they killed during a rampage more than 130 years ago.

The mobs were out to break a month-long strike by sugar plantation field hands, many of them former slaves. The striking sugar workers wanted a raise and wanted cash instead of chits usable only at one plantation's company store.

As tensions rose, a judge declared martial law in Thibodaux. When violence finally erupted on Nov. 23, 1887, white mobs went door-to-door for more than two hours shooting unarmed blacks, said John DeSantis, who wrote a book about the killings. An estimated 30 to 60 African-Americans are believed to have been killed in what became known as the "Thibodaux Massacre."

DeSantis created a committee including descendants of the massacre's victims, as well as descendants of Confederate and plantation families, to honor those victims and possibly find their remains.

A Tulane graduate student, Davette Gadison, is in charge of the initial survey, though a geology professor will run the radar. Gadison's experience with mass graves includes a month helping a forensic team excavate and analyze remains of people killed during the civil war in Guatemala and about the same amount of time doing similar work in the East African region called Somaliland.

She will use ground-penetrating radar to look for disturbed earth on land now owned by an American Legion chapter built by African-American veterans during the segregated 1950s, and a vacant lot next door to it.

The building was erected over a city landfill. According to local lore, the same lot had been used decades earlier to dump the bodies. Bones won't show up on the radar, but it might show areas of disturbed earth underground — areas where bodies might have been buried. If bodies were buried there, they might be in a trench, a deep circle, or a wide but shallow grave, Gadison said.

If the ground-penetrating radar picks up something of interest, they can investigate further with limited coring — pushing a long cylinder into the ground to pull out a section of the earth, which Gadison can then analyze.

If there's a mass grave, the committee wants to have any remains exhumed, investigated, and buried in consecrated ground.

But if any bones turn up Thursday or Friday, all work would halt while Gadison applies to the state archaeologist for permission to continue.

Thibodaux is about 60 miles west of New Orleans.